In a wet lay process for the production of nonwoven webs, short cut staple fibers, either natural, synthetic, or a blend of same are dispersed in an aqueous medium to produce a fiber slurry. A chemical binder is added to the slurry or to the formed web to promote bonding of the fibers into a unified structure. The fiber slurry is fed to a paper making machine, such as a Fourdrinier machine where it is positioned on a porous support. Suction is applied beneath the porous support and removes the majority of the aqueous medium from the slurry, leaving a damp web of fibers across the forming area. The newly formed web is then further processed to yield a final nonwoven web where the fibers are bound to adjacent fibers to define a unitary structure.
A nonwoven web produced by the wet lay process can be only as good as the initial fiber dispersion. The fiber dispersion determines uniformity across the width of the web, the presence or the absence of voids in the web, later bondability of the fibers into a unitary structure, and the presence or absence of globs of fiber in the web. It is therefore quite important that a proper fiber dispersion be achieved to produce a good fiber slurry and thereafter, that the fiber slurry be properly processed to realize a quality nonwoven web.
Previously, various materials have been added to the fiber and/or the aqueous medium in which the fiber is dispersed to attempt to produce a good fiber dispersion. Several criteria are important to the formation of this fiber dispersion. For example, it is necessary to avoid substantial foaming in the aqueous bath. Foaming produces entrapped air in the slurry, which if carried through the nonwoven forming process will produce voids in the ultimately formed web. Likewise, should a group of fibers be present in the slurry formation, adhering to each other and not individually dispersing, clumped fibers will appear in the web as a glob or thickened portion which is visually apparent. Still further, as mentioned above, chemical binders are employed to promote the adherence of individual fibers to adjacent individual fibers and thus provide a unitary nonwoven structure. In forming the fiber slurry, care must be taken to avoid the introduction of any ingredient into the aqueous medium that tends to promote foaming, or to reduce the dispersibility of the fiber, or that will chemically or mechanically adversely affect the efficacy of the binder that is utilized. Also the composition should not interfere with other ingredients of the aqueous medium, such as viscosity builders, wetting agents, and the like.
The prior art is generally deficient in affording a proper fiber dispersion or slurry for the ultimate formation of the nonwoven web due to a deficiency in one or more of the above noted criteria. The present invention, however, overcomes shortcomings of the prior art, in that, a finish or dispersing composition is disclosed herein that permits the formation of a highly superior fiber dispersion that is low foaming, has virtually no fiber clumps and does not hinder fiber bondability. The present composition thus leads to the ultimate formation of a uniform and high quality nonwoven web.
In general in a wet lay process, short cut staple fibers are provided to the nonwoven manufacturer. The nonwoven manufacturer, of course, has its own formulation for the white water into which the staple fibers are to be dispersed. Such formulations generally include surfactants, viscosity control agents and the like. Two particular systems are set forth in U.S. Pat. Nos. 4,007,803 to Ring et al and 4,049,491 to Brandon et al. Both Ring et al and Brandon et al disclose the addition of surfactants, e.g., alkylaryl polyether alcohol types (octyl phenol series) to achieve a white water surface tension of 30-35 dynes and emulsion stabilizers, e.g., natural or synthetic gums. The aqueous medium of the above noted patents is agitated to create tumbling water surface conditions in which up to, but less than about 4 percent by volume of air is entrained in the water in the form of tiny bubbles. The fibers are dispersed without excessive foam generation.
Short cut fibers of the present invention when utilized with a system of the type generally set forth in the above noted patents, affords an improved web from the standpoints of absence of voids, absence of clumps of fiber, and overall web uniformity. In like fashion, anionic surface active agents as disclosed herein afford similar advantage when the staple fiber as a finish component or when added separately to the white water, or dispersing medium.